Planting forests as carbon sinks is a familiar idea. Less discussed - but potentially even more significant - is the possibility of locking vast quantities of carbon into the soils of the world's dry grasslands. This could be achieved by changing the way we graze cattle and by adding more grazing animals in regions that currently have none, according to advocates Tony Lovell and Bruce Ward.

In naturally functioning grasslands – the Serengeti being a rare surviving example – huge herds of grazing animals such as wildebeest are constantly moving and closely packed together as defence against predators.

When a herd grazes an area, the grasses get shortened and shed parts of their carbon-rich roots into the soils. But the herd quickly moves on, giving the grass a chance to grow back, pulling CO2 from the air. The result is a giant biological pump that takes carbon from the atmosphere and moves it safely to the soils, where it adds to productivity and supports biodiversity.

In contrast, most domesticated cattle are kept in small herds that are stocked for long periods in the same place – a practice that doesn't encourage healthy grasses. If farmers switch to grazing practices that mimic the movements of wild herds, this can easily increase the proportion of carbon stored in dry soils from 1% to 2%, according to Lovell and Ward. This is sufficient to remove 100 tonnes of CO2 from the atmosphere for each hectare of land.

Even when the methane and nitrous oxide emissions of the cattle are taken into account, this "regenerative grassland management" holds the potential to significantly reduce the amount of greenhouse gas in the air.